Yes.In order to be able to produce breastmilk you have to have developed mammary glands in response to hormonal and chemical changes in the body. . . and so forth. Numerous things - like other health issues - can halt and inhibit this process.
I'm not sure what you mean by "mental problems", but many women are traumatized from negligence.You're talking as if every mother who has issues has mental problems or negative connotations with nursing - why do you assume this?
Right.A lot of women don't have problems at all with the concept - nothing negative what so ever . .. but might still have physical issues that inhibit the process.